DERIVATIVE INSTRUMENTS - Fair Value of all Derivative Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Assets	$ 49,718	$ 80,893
Liabilities	42,546	74,652
South Jersey Gas Company
Derivatives, Fair Value [Line Items]
Assets	7,666	5,807
Liabilities	11,815	8,737
Commodity Contract
Derivatives, Fair Value [Line Items]
Assets	49,718	80,893
Liabilities	0	0
Commodity Contract | South Jersey Gas Company
Derivatives, Fair Value [Line Items]
Assets	7,666	5,807
Liabilities	0	0
Derivatives not designated as hedging instruments under GAAP
Derivatives, Fair Value [Line Items]
Assets	49,718	80,893
Liabilities	42,546	74,652
Derivatives not designated as hedging instruments under GAAP | South Jersey Gas Company
Derivatives, Fair Value [Line Items]
Assets	7,666	5,807
Liabilities	11,815	8,737
Derivatives not designated as hedging instruments under GAAP | Commodity Contract | Derivatives - Energy Related - Current
Derivatives, Fair Value [Line Items]
Assets	42,068	72,391
Liabilities	26,910	60,082
Derivatives not designated as hedging instruments under GAAP | Commodity Contract | Derivatives - Energy Related - Current | South Jersey Gas Company
Derivatives, Fair Value [Line Items]
Assets	7,608	5,434
Liabilities	4,467	1,372
Derivatives not designated as hedging instruments under GAAP | Commodity Contract | Derivatives - Energy Related - Non-Current
Derivatives, Fair Value [Line Items]
Assets	7,650	8,502
Liabilities	4,359	4,540
Derivatives not designated as hedging instruments under GAAP | Commodity Contract | Derivatives - Energy Related - Non-Current | South Jersey Gas Company
Derivatives, Fair Value [Line Items]
Assets	58	373
Liabilities	69	0
Derivatives not designated as hedging instruments under GAAP | Interest rate contracts | Derivatives - Other - Current
Derivatives, Fair Value [Line Items]
Assets	0	0
Liabilities	798	681
Derivatives not designated as hedging instruments under GAAP | Interest rate contracts | Derivatives - Other - Current | South Jersey Gas Company
Derivatives, Fair Value [Line Items]
Assets	0	0
Liabilities	398	386
Derivatives not designated as hedging instruments under GAAP | Interest rate contracts | Derivatives - Other - Noncurrent
Derivatives, Fair Value [Line Items]
Assets	0	0
Liabilities	10,479	9,349
Derivatives not designated as hedging instruments under GAAP | Interest rate contracts | Derivatives - Other - Noncurrent | South Jersey Gas Company
Derivatives, Fair Value [Line Items]
Assets	0	0
Liabilities	$ 6,881	$ 6,979